Power hammer



Oct. 29, 1963 H. c. GUSTAFSON 3,108,644

POWER HAMMER Filed May \16. 1960 5 I 23 mmvrox IFIIG. 3. HJALMERC,GUSTAFSON ATTORNEY United States Patent ()fiice v awash Patented Oct.29, 1963 3,108,644 PGW'ER HAMMER Hjalmer Q. Gustafson, Denver, (Zola;Hazel A. Gustaison, heir to Hjahner (I. Gustatson, deceased Filed May16, 1960, Ser. No. 29,339 1 (llaim. (til. $73-$18) This inventionrelates to high-energy impact tools, and more particularly to portabletools utilizing a high speed rotary shaft for actuating a short-stroke,high rate of impact power tool for breaking, chipping, drillingoperations, etc.

Portable, power-driven impact tools, frequently called power hammers,have been proposed in many forms. In recent years electric motors havebeen the main power source for such portable hammers, but essentiallyall have been based on a theory of operation of using a heavy impactmember with a relatively slow rate of impact of the weighted member onan operating tool. Further, such electrical tools transmit the rotaryaction of an electric motor shaft into a reciprocal motion of the weightmember by means of rotary cams with dropping followers operated directlyfrom the motor shaft. In such tools there is a high degree of wear and ashort operating life of the parts, particularly due to the frictionbetween the cam and the cam follower and the impact produced betweenthese same parts.

Under dusting and gritty conditions of drilling and chiseling the Wearis greatly accentuated. Such tools are, further, subject to destructivevibration unless the impact of the hammer is directed against a toolwhich is in operative position against a working face. In other words,operating the hammer free from a work face will actually producedestructive vibrations which can destroy the power hammer in arelatively short time.

According to the invention, I have provided a highenergy, low-vibrationhousing, power hammer which uses a very low-throw eccentric cross headon a high speed shaft to drive an impact member at a short-stroke, veryhigh frequency rate. The low-throw cross head provides a high speedreciprocal motion of a Weighted member, through an indirect connection,in the form of a relatively stillhelical spring between the cross headand the hammer member. This arrangement reduces the number of parts, theweight and the impact forces on the parts. The spring connector greatlyreduces vibrations being transmitted to the mechanism housing. There is,also, provided an impact member mounted in a series of shaped bores inan arrangement forming an air cushion against which the energy of thehammer member may be expended in the absence of an operating tool.

Included among the objects and advantages of the present invention is ahigh-energy, low-vibration power hamrner of very lightweight forbreaking, chipping, drilling and similar operations. The tool isprovided with a relatively stiff spring connecting member between alowthrow, high-speed cross head and a hammer member arranged to strikean operating tool at a high frequency so that the energy of the impactis directed onto the tool and is essentially not transmitted to the toolhousing. The device, furthermore, provides a power hammer ofsubstantially reduced number of parts to thereby reduce wear of theparts and maintenance of the tool. The device includes an impact memberwhich with passages in the housing provides an air cushioning for thestriking hammer of the device to thereby prevent free cycling of thehammer member, and to prevent transmission of destructive vibrations tothe tool housing when running without an operating tool.

These and other objects and advantages of the invention may be readilyascertained by referring to the description and appended drawings inwhich:

FIG. 1 is a side elevational view, in partial section, of an impact toolaccording to the invention arranged in operating position against atool;

FIG. 2 is another side elevation of the device of FIG. 1 taken alongsection line 2- .2;

FIG. 3 is a detailed view of an operating position of a cross head ofthe device;

FIG. 4 is an enlarged detailed view of the impact member in operablearrangement with a tool according to the invention;

FIG. 5 is a detailed view of the impact member of the device shown inoperative position without an operating tool;

FIG. 6 is a cross section of a tool retainer taken along section line6-6 of FIG. 2 showing a tool retaining position; and

FIG. 7 is a cross section similar to the cross section of FIG. 6 withthe tool retainer in tool removal position.

The description of the device is set forth in relation to a flexibleshaft operated device, however, it is obvious that a direct connectedelectric motor could be mounted on the device in the same relation as toits housing as the flexible shaft. It is, therefore, to be understoodthat the description is intended for illustration only and not to limitthe spirit or the scope of the invention to the precise details setforth in the following description.

In the device illustrated in PKG. 1, the high-energy power hammerincludes a lower housing l threadedly engaged to an upper housing 2. Apin 3 connects the two housing members together insuring positiveretention of the parts under the vibration forces of the impact device.The pin 3 is mounted on a circular retaining spring 4 which is mountedin rabbets 5 and 6 on housings 2 and 1 respectively forming a groove inposition to hold the spring and thus retain the pin 3. The housing 2 isprovided with a manipulating handle 7 at one end and a tool bore 8 atthe opposite end. A shaft housing 12 is secured to the upper housing 2by means of bolts 14, and a shaft 15 is journaled for rotation therein.The inner end of the shaft 15 includes an eccentric shaft 16, which isonly slightly offset from the axis of the shaft 15. The outer end of theshaft 15' includes a rectangular bore 17 into which a rectangular drivemember 18 may be inserted for driving the shaft. The rectangular drivemember 13 is mounted on the end of a rotary flexible shaft 19' which isretained in position on the housing 12 by means of a screw cap 20. Theopposite end of the flexible cable 19 is, obviously, mounted and rotatedby an electrical motor, which is not shown, and for safety a cover orsheath 21 is provided over the flexible shaft 19.

A cross head 25 is mounted on the eccentric member 16 by means of abearing set 26, FIG. 2, so that the cocentric shaft 16 freely rotates inthe cross head 25 which is maintained essentially non-rotary. A boss 27is integrally mounted on the cross head 25 and extends toward the toolbore 8. A relatively stiff helical spring 28 is securely mounted on theboss 27 by means of a tight frictional fit or in some instances bythreading the spring on threads on the exterior of the boss 27.

The housing member 1 is provided with a bore 39, in which is mounted areciprocal impact or hammer member 31. The impact member is arranged forfree reciprocal movement within the bore. A-boss 34 integrally mountedon the impact member 31 is securely mounted in the spring 28 in a mannersimilar to the spring connection with the cross head. The lower end ofthe bore 30, toward the tool bore, is provided with a short, smallerdiameter bore portion 33. The end opposite the boss 34 on the impactmember 31 is provided with an integrally or securely attached extension37 which is arranged with essentially close fit in bore 33, but isreciprocable therein. As the impact member 31 operates in the bore 30,the parts should be maintained well lubricated, and the extension 37 is,likewise, lubricated for movement in the short bore portion 33. Thelubrication, also, provides for the maintenance of the air cushion, asexplained below.

Since the device is a portable power hammer, it is convenient to providea switch for the electric motor, which rotates the flexible shaft 19, atthe hammer itself, and for this purpose an on and off switch member 45}is provided on the handle 7. This switch member connects and disconnectsthe leads of an electric cable 41 which is interconnected with theelectric motor power leads. In the event the flexible shafit is replacedby a direct connected electric motor, the power line 41 would normallybe connected to the motor attached to the housing.

A drill, chisel or other type of tool is arranged for insertion into thetool bore 8 according to conventional means. In this instance, a drillsteel is provided with a shaft 56*, an impact ring 51 and a square shank52, which is arranged for mounting in the square bore 8. The shankportion includes a notch 55 into which a retaining member or pin 53falls for temporarily locking the tool in the tool bore. A cylindricalspring 54 retains the pin 53 in the notch 55 for holding the tool. It isto be noted that the notch 55 is sufiiciently long to permit reciprocalmovement of the drill steel in the tool bore. Further, the end of theshank is bevelled to aid insertion of the shank past the pin.

As illustrated in FIG. 6, the drill steel shank 52 is mounted in thesquare tool bore 8 with the member 53 mounted in the groove 55. Themember 53 is held by circular spring 54 holding the drill steel in thehammer. In FIG. 7 the drill steel is either being removed or insertedand the member 53 is riding on an edge of the shank in upper positionout of the notch 55'.

In one very convenient size a quarter pound impact member, which ismember 31 with attached boss 37, is oscillated by a shaft 19 rotating atat least about 7200 r.p.m. or higher. In this instance, the offset oreccentric shaft 16 is oifset of an inch 50 that there is a sixteenthinch throw at and 180 of the cross head which in turn oscillates thehammer at about /s of an inch. As shown in FIG. 3, the eccentric is in a90 position illustrating that the angular deflection is only about 4,which is easily accommodated by the bending of the spring. At the highspeed at which the hammer operates, the energy of the impact on the toolis sufficient to effectively drill, chip, chisel or otherwise utilizethe impact energy. At this high speed and low throw there is essentiallyno vibration, especially due to the spring connection between the crosshead and the hammer. The spring provides a flexible connection whichpermits the lateral movement of the cross head and the reciprocalmovement of the impact member.

When the drill steel, or other tool, is in place and the hammer ispressed against it by the operator bearing down on the handle, operationof the hammer imparts the energy of the high frequency impacts to thework face, that is, any surface being acted on by the tool. So long asthe operator bears against the tool, the shank contacts the impactmember on its stroke away from the cross head.

In the event that the tool is operated without the drill steel pressedagainst a work face, or if no tool is attached to the hammer, themovement of the impact member tends to cause it to over run its normalreciprocal movement. This over running causes boss 37 to enter bore 33trapping air in the annular space between bore 30 and the boss 37. Thisair is compressed damping the movement of the impact member, andabsorbing the energy of the movement. This prevents undue vibrations andprevents transfer of the full force of the impact to the housing. As thecross [head pulls the impact memher back for another impact movement,the dead air pocket is opened and heated air (due to the compression)escapes, thus preventing over heating of the tool. Thus the combinationof the spring connector and the air cushion provides means fortransmitting impact forces to an operating tool, but cushions suchimpact forces in the absence of such tools.

Light weight, portable power hammers may be effectively made using theweights and speeds outlined above, and where desirable, the speed may beincreased or the size and weight of the parts may be changed.Maintenance is obviously simple since there are few moving parts and nocomplicated moving structural parts.

Having thus described my invention, what is desired to be secured byUnited States Letters Patent is:

A power hammer of the class described comprising a housing having amanipulative handle at one end and a tool holding passage at theopposite end, a main bore in said housing communicating with said toolholding passage, said tool holding passage being of substantiallysmaller dimensions than said bore, a relatively light weighted hammermember reciproca'oly mounted in said main bore, a cylindrical extensionsecured to said hammer in tool striking position, said main boreincluding a stepped down bore adjacent said tool holding passage forreciprocably accommodating said extension, there being a shoulderbetween said step-down bore and said main bore, a low-throw eccentricshaft mounted in said main bore, a cross head mounted on said shaftadjacent to and spaced from said hammer member, a relatively stiifspring secured to and interconnecting said cross head and said hammermember, means for rotating said shaft at a high speed of at least about7200 r.p.m., and said extension arranged to move cyclically from aposition out of said stepped down bore into said stepped down bore fortrapping air between said cylindrical extension and said main bore onover-travel of said hammer member to cushion the impact of said hammermember in absence of an operating tool.

References Cited in the file of this patent UNITED STATES PATENTS1,625,211 Jones Apr. 19, 1927 2,240,598 Wilke May 6, 1941 2,613,662Reynolds Oct. 14, 1952 FOREIGN PATENTS 718,582 Great Britain Nov. 17,1954

